The present invention relates generally to signal processing circuits and communications network devices and, more particularly to a system for channel estimation in a wireless communication network.
Wireless communication systems are well known. For example the 3rd Generation (3G) of mobile telephone standards and technology developed by the 3rd Generation Partnership Project (3GPP™) has generally been developed to support macro-cell mobile phone communications. Such macro cells utilise high power base stations (NodeBs in 3GPP parlance) to communicate with wireless communication units (or User Equipments (UEs)) within a relatively large geographical coverage area.
Lower power and therefore smaller coverage area cells are a recent development within the field of wireless cellular communication systems. Such small cells are deployed for effective communication in coverage areas supported by low power base stations. The terms “picocell” and “femtocell” are often used to mean a cell with a small coverage area. Herein, the term “small cell” means any cell having a small coverage area and includes “picocells” and femtocells. These small cells are intended to augment the wide area macro network and support communications to UEs in a restricted, for example, indoor environment.
Communications systems and networks are developing towards a broadband mobile system and the 3rd Generation Partnership Project has proposed a Long Term Evolution (LTE) and an advanced (LTE-A) solution where a UE communicates over the wireless link with an evolved Node B (eNode B). The low power base stations (or ‘access points’) that support small cells in LTE are sometimes referred to as Evolved Home Node Bs (eHNB). OFDMA (orthogonal Frequency Division Multiple Access) and SC-FDMA (single carrier FDMA) access schemes were chosen for the down-link (from NodeB to UE) and up-link (from UE to NodeB) respectively in the LTE system. UEs are time and frequency multiplexed on a physical uplink shared channel (PUSCH).
One uplink reference signal, the Sounding Reference Signal (SRS) is defined in support of frequency dependent scheduling, link adaptation, power control and uplink synchronization maintenance, which are functions handled above the Physical Layer, mainly at layer 2. The main purpose of the SRS is to allow the eNodeB to estimate a UE's radio channel information on time and frequency resources possibly different from those where it is scheduled. SRS is typically used to estimate channel estimates and gains across the system bandwidth, Noise Variance (NV), timing offset, frequency offset, Doppler offset and other channel state parameters. SRS processing typically computes a signal to interference plus noise ratio (SINR) measurement from the channel estimates and noise variance. However, current computational methods for deriving useful metrics from the SRS are not always optimum for macro cell scenarios where there are few users or for small cell applications. Furthermore, the FAPI (Femto Application Platform Interface) initiative stipulates that an estimation of SINR be done on a per resource block (RB) basis. However, this requirement consumes significant processing resources.
Therefore it would be advantageous to provide a means for improving the reliability of an estimated CIR and SINR with reduced computation complexity.